Studies focused on the cellular control of nucleoside diphosphate hexoses, which are precursors or hyaluronic acid (HA) synthesis, and on the regulation of HA synthesis, a glycosaminoglycan that is associated with tumor invasion and metastasis. Several agents were found that inhibit HA production by fibroblasts: suramin, vanadate, and the nonsteroidal antiinflammatory drugs indomethacin and mefenamic acid. These agents inhibit HA synthesis without inhibiting DNA synthesis, thus HA synthesis can be dissociated from processes involved in cell proliferation indicating that the metastatic and invasive properties of malignant cells might be controlled by non-cytotoxic agents. These data suggest that one mechanism responsible for suramin's effectiveness against prostatic carcinoma and the nonsteroidal antiinflammatory drug's effectiveness in inhibiting the progression of certain human carcinomas may be related to their ability to block tumor-associated HA synthesis, which is a component of tumor progression. Studies were continued on the characterization of HA synthesis and release by fibroblasts. Electron microscopic measurements of the length of HA molecules allowed the calculation of rates of elongation, completion, and release, as well as the number of molecules attached to the cell surface. These determinations, along with enzyme kinetic data on hyaluronic acid synthetase, suggest that one enzyme molecule is responsible for the synthesis of one HA chain; a novel mechanism for the cellular regulation of HA synthesis. A rapid and sensitive assay for HA in biological samples was developed. This method utilizes a 96-well plate assay and can accommodate a large number of samples. The method is currently being extended to allow the location and quantitation of HA in tissue sections.